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As they have with the Great Depression, economic historians will argue for decades about the origins of our current crisis. But, surely, we can agree that the failure of international economic cooperation in the early 1930s—and worse, the sequential adoption of beggar-thy-neighbor domestic policies—made matters worse at a time when enlightened statesmanship could have made them better for everyone. Similarly, the current crisis is not just a U.S. problem or a European problem; it is a global problem that requires a coordinated global response. “We’re all in this together” is not a moral bromide, in this instance, but a simple statement of fact.

Since the crash of 2008, the entire world has relied on a shared, if tacit, plan to avert all-out catastrophe and a...